The present invention relates generally to programmable resistance memory elements. More specifically, the present invention is related to a method of programming a programmable resistance element.
Laser blown fusable links have many applications in integrated circuit technology. For example, laser blown fuses may be used in memory arrays to repair bad memory cells with redundant memory cells. If some of the memory cells in a semiconductor memory device are found defective in a testing operation, the defective memory cells are identified and replaced with reserve memory cells in the redundant circuits as necessary. In this manner, the defect of the semiconductor memory device is repaired. To activate the reserve memory cells in the redundant circuits (i.e., to use the redundant memory cells), after the defective memory cells are identified, they need to be electrically disconnected from the memory cell array and furthermore, the redundant or reserve memory cells need to be electrically connected to the same array instead. Such switching or replacement of electrical connection are typically realized by disconnecting specific wiring lines by opening xe2x80x9crepair fusesxe2x80x9d provided beforehand in the device as necessary.
In addition to repairing bad memory cells, laser blown fuses may also be used for the customization of an integrated circuit to give it special characteristics. For example, fuses may be used to program non custom programmable devices. Fuses may also be used for identification purposes such as to store information about an integrated circuit or mark an integrated circuit in a manner that is readable visually or electrically, for example serialization of the integrated circuit, or how the device is configured by the laser. Laser blown fuses are typically opened by being irradiated by a laser beam during a process called xe2x80x9claser trimmingxe2x80x9d.
Laser blown fuses have several inherent disadvantages. These include high capital cost, floor space, and manufacturing time required for the tools and process used to laser blow the links. Also laser blown fuses must be blown (i.e., opened) prior to final product packaging. This rules out die customizing at later steps in the manufacturing process or in the field by the customer. Laser fuses take up significant die area, limiting the number of fuses that can practically be used.
Programmable resistance memory elements formed from programmable resistance materials that can be programmed between at least two electrical resistivities in response to electrical signals are known in the art. Such programmable resistance elements may be programmed to a high resistance state to store, for example, a logic ZERO data bit. As well, they may be programmed to a low resistance state to store, for example, a logic ONE data bit.
One type of material that can be used as the programmable resistance memory material for programmable resistance elements is a phase change material. Phase change materials may be programmed between a first structural state where the material is generally less ordered (for example, an amorphous state) and a second structural state where the material is generally more ordered (for example, a crystalline state). The less ordered structural state exhibits a higher electrical resistivity than the more ordered structural state. Phase change materials may also be programmed in incremental steps reflecting (1) changes of local order, or (2) changes in the relative volume of materials having different local order so as to provide a xe2x80x9cgray scalexe2x80x9d represented by a multiplicity of conditions of local order. The use of electrically programmable phase-change materials is disclosed, for example in U.S. Pat. No. 5,116,758, the disclosure of which is incorporated by reference herein. Other examples of phase-change materials and memory elements are provided in U.S. Pat. Nos. 5,296,716, 5,414,271, 5,359,205, 5,341,328, 5,536,947, 5,534,712, 5,687,112, and 5,825,046, the disclosures of which are all incorporated by reference herein.
The present invention is directed to a method of operating a programmable resistance memory element so that the programmable resistance memory element may be operated as a fuse. Hence, a fuse is achieved through programming of a programmable resistance memory element rather than through the special requirement of a laser or special thin film.
One aspect of the present invention is a method of operating a programmable resistance element having at least a low resistance state and a high resistance state, the method comprising the steps of: providing the programmable resistance element, the element including a programmable resistance material; and applying energy to the programmable resistance material sufficient to transform the programmable resistance element to a condition wherein application of additional energy is unable to transform the programmable resistance element to the low resistance state.
Another aspect of the present invention is a method of customizing an integrated circuit, the integrated circuit including a first circuit coupled to a second circuit through a programmable resistance element having at least a low resistance state and a high resistance state, the element including a programmable resistance material, the method including the step of: applying energy to the programmable resistance material sufficient to transform the programmable resistance element to a condition wherein application of additional energy is unable to transform the programmable resistance element to the low resistance state.
Another aspect of the invention is an electrically programmable memory array, comprising: a plurality of programmable resistance elements having at least a low resistance state and a high resistance state, at least one of the elements being in a condition such that applying energy to the element in the condition is unable to transform the element in the condition to the low resistance state.